Apparatus for manufacturing fuses



Aug. 3l, 1954 R. coLoMBo APPARATUS FoR MANUFACTURING FUsEs Filed Feb.19, 1948 FIG; 1

Ill l 7\ A m w. W

Patented Aug. 31, 1954 UNITED STATES PATENT OFFICE Roberto Colombo,Turin,

Italy, assignor to Lavorazione Materie Plastiche (L. M. P.) di M. I.Colombo & C.Societa in Accomandita Semplice, Turin, Italy ApplicationFebruary 19 In Italy Octob Section 1, Public Law Patent expires 0 2Claims.

This invention relates to apparatus for manufacturing matches or fusesfor all civilian uses in which explosives are employed, such as blastingor road building, mining, demolition and the like.

It is known that matches or fuses for such purposes generally consist ofgunpowder or special explosive mixtures, enclosed in a tubular casingformed by helical wound textile threads. As a rule, a plurality ofhelical windings are made with alternately right-handed and left-handedthread. Between the textile layers gums or solutions thereof or othermaterials are interposed in order to hold together the threads of thevarious layers and form a sheath withstanding bending or slight tensilestresses. The solution of gum or other material further tends withincertain limits to protect the 'match or fuse against moisture, but thisresult is in practice hardly satisfactory, for an exposure of matches orfuses of this type to moisture makes them useless or, at least,seriously impairs their eiiiciency. Moreover, with a coating of thiskind the matches or fuses treated with gums or other special mixturestend to expand when the matches or fuses are subjected to small radiuscurves or frequent bending in course of laying, which often makes thematch or fuse inoperative. Finally, the coating requires a lengthyoperation, as gums, paints or the like should be allowed to dry afterthe formation of each helical layer before the next layer is begun.

A further coating in use for matches or fuses consists of a sheath ofsoft lead, within which the explosive material is compressed. Thiscoating also has various disadvantages in practice, among which the mostserious is certainly the low resistance to frequent bending, moreparticularly at acute angles. In this case, on account of the materialof which it is constituted the coating tends to crack and operation ofthe match or fuse is generally impaired. If the coating is well made thematch or fuse is safely protected against moisture, but it can only bemanufactured to limited lengths, which are in many cases insuiiicientfor practical use. The manufacture of this match or fuse is carried outby successive drawing of sections of tubes of lead or lead alloys, inwhich a certain quantity of gunpowder has previously been filled.Successive drawing operations of lead with the explosive therein, while50 1948, Serial No. 9,584 er 4, 1944 690, August 8, 1946 ctober 4, 1964they gradually reduce the inner diameter of the tube and its thicknessaccordingly, also eiect a certain compression of the gunpowder packingthe latter. Frequent drawing operations are, however, necessary and,apart from the considerable unavoidable waste, the production of tubesections of considerable length is not possible.

A further known match or fuse coating consists of interwoven threads,instead of threads helically wound about the blasting charge. Theinterwoven layer is coated with a waterproof paint which protects, to acertain extent only, against moisture. The chief drawback of thiscoating is that on close bending the hose may be strangled, the match orfuse interrupted so that the unit becomes inoperative, for the materialcomposing the outer hose is not elastic.

A considerable improvement over the above types of matches and fuses isa fuse having a coating of synthetic substances. Said syntheticsubstances are preferably thermoplastic materials, for instance productsof polymerisation and mixed polymerisation of vinyl compounds,polycondensation products, such as polyamides or polyurethanes, andpolymerisation products of acryl, styrol compounds, and the like, orsoftened cellulose acetate or ethylcellulose compounds.

Since thermoplastic materials are generally slightly elastic, whichmight result in objectionable discontinuties under considerable tensilestreses of the inner explosive lling of the match or fuse, the coatingis reinforced by means of strong longitudinal threads, for instance ofnatural or articial silk or, better, of polycondensed resins of theamino group such as nylon.

The advantages of the fuse having an outer coating of thermoplasticmaterial, reinforced by means of longitudinal threads, are as follows:

(1) The fuse is absolutely water-proof even if steeped in water or otherliquids;

(2) The coating is protected against acids, bases, oils, fats, salinesolutions, sea water, etc.;

(3) The fuse can be bent even to a loop without any danger of damagingeither the coating or the explosive charge contained therein;

(4) The reinforced coating provides a high resistance against tensilestresses and small elongation;

(5) The fuse can be permanently colored, using colored matter mixed withthe synthetic substances forming the outer layer.

The invention relates to an apparatus for manufacturing fuse having anoute-r layer of thermoplastic material provided with reinforcing threadsof high tensile strength. The apparatus according to the inventionaffords the possibility of manufacturing said fuse in one operation andof any desired length. The thermoplastic material is processed in anyknown manner, but preferably by means of extrusion. machines of thescrew press type, and the hardness and flexibility of the coating can bevaried 'by` suitably admixing the raw material with particularsubstances of various types, such as plasticizers or softening agents.

The apparatus is described with reference to accompanying drawings, inwhich Figures 1 and 2 show a part axial section and cross section of thefuse, Figure 2 shows the bored head for manufacturing the reinforcedfuse and- Figur-,elfi isa diagrammatical View of the apparatus.

The fuse, Figures 1 and 2, comprise a core l of explosive materialenclosed in a sheath 2 of synthetic material in whichstrong threads 3(for instancenylon) of low elongation areembedded in a` longitudinaldirection.

The device for manufacturingthe reinforced fuse isshown diagrammaticallyin Figure 3 and comprises an extrusion head I formed withan axial borel, and witha pressure die of Iannular form ,5 concentrcwithfthe bore landan inner annular chamber i ,to which `the synthetic materialadaptedto form the sheathZ is fed bythe s crew press 5I (Figure 3) nxed at ,Thechamber Yl has conveniently mounted therein a bush for distributing thematerial fed by the press. The sheath materialis forced underpressureto- Wards the pressure die 5. rAt the same time through holes tarranged in a circular row inthe rearlportion of the extrusionheadr Il)along a circle equal in diameter to thezmiddle diameterof the pressuredie, nylon threads 5, adaptedto :form the armature for the matchor-fusesheath, zare conveyedinto the chamber ,6 towards the pressure die. Thematerial is extruded through the `annular ,pressure die incorporatingthe .nylon threads therein,v said nylon threads unwinding from spools 55on thebutercasingof -the1ex trusionhead lf3. Atthesame time theexplosivechargezis Afed to the device lpthroughthecentral hole ,l in theextrusion head iii. The synthetic: material issues .throughthe extrusionhead I-Eliin cylindrical form whichis drawn either by virtue of its ownweight or by otherzmeans. The traction of the still hot materialissungfrom. the pressure die causesthe hose to contract and4 come thereby.into contact with the core of explosive materialissuing from the axialbore l in theiextrusion head llt-form the coating whichy exerts a slightpressure on the explosive. A short distance from the pressure'die, asthe coating has cooled down,'the-match orfuse is denitely'formeditsmanufacture being lobviously continuous and very rapid.

The explosive material may be introduced into therhole -1 either througha-hopper or bylmeans of a screw press or a cylinder and piston device.The latter preferably consists of a pairof cylinders and pistons toensure a continuous feed, If the explosive material is in powder, grain,flake or plateform or the like,'itwill be possible to employ a bindingagent adapted to hold the particles together and preventthe explosivefrom slipping 4 out when the match or fuse is cut. 'Ihe binding agentmay likewise be a synthetic material.

In certain cases it may be preferable to employ instead of a continuousexplosive core, preformed 5 blocksI or cylinders of explosive of smalllength conveniently threaded on a thread for instance of polyamideresin. These blocks, connected together by the thread, are introducedthrough the hole 1, kcaught by :the coating and carried along l therebyas they are incorporated therewith.

When the operation is completed, the resin thread 1 connecting theblocks may be removed.

-In-most cases, however, the explosive is in power or grain form, and it1s then preferable to l lemploytwo extrusion presses, one of whichcompresses the, explosive material. A compression of the powder'is inany case necessary for avoiding `the above mentioned drawback that thepowder may pourout ofthe. coating when the match or yfuse is cut tolength. When compression of the powder is insufcient, a binding agent asmentioned above is admixed thereto for holding together the granules ofwhich it is made. Syntheticrresins as binding agents may be admixed withthe powder. v

Inother cases it 1 is possible :to 4employpJ :paste of explosive powder:which can'bewell. compressed in the extrusion press.

What I claim is:

1. Apparatus for manufacturing fuses havingya sheath of thermoplasticVmaterial Vcomprising Lin combination an annular chamber, means forifeeding thermoplastic material to'said annularrchamber, an annularextrusion die coaxial .with-said annular chamber, means .for feedingthreads :of

synthetic material to saidannular chamber to,be embedded in thethermoplastic material, means for .extruding a pipe Vof thermoplastic:material havingdncorporated A.therein the threads 'of'syn- 40 theticmaterial arranged.parallelftoithesaxisfof the Vextruded pipe, Van innerextrusion die .co` axial with said, annular chamber,-means:5for; feed-`ing an explosive charge to saidfinn-er extrusion die, .thecross-sectional iarea ,of vthe linner ex, 5 trusiondiebeing. smallerthan thercross+sectional area of :the ,annularfextrusion die, thefpipepof,

thermoplastic material coming; into contact withA the continuous ooreofexplosive charge,.andeex.

erting a slightpressureon it byqefectofwa trav. tion exerted` on saidpipe when-hot. 2. Apparatus for manufacturingzfuses l'raving-a sheath of`thermoplastic material comprising Yin combination an annular. chamber;meansfforfeedingthermoplastic material to said: annular'chamber,yanannular extrusion die coaxial withisaid: annularchamber, means forfeeding threads of synthetic material yto.` said annular chamberxto'beembedded `in the A.thermoplastic imaterial, :meansA for `extruding fagpipe of thermoplastic :material from said extrusion die v.havingincorporated, therein the threads of synthetic material arrangedparallelrtoy the axis of .the extrudedpipefand.y along the edgesof aregularprism, an inner .cylindrical extrusion die coaxial withIthefsaid. annulanchamf ber, means for: feeding anI explosive charge,tosaid inner extrusion die, means for extrudingva cnn tinuous core ofexplosive `material `from ,said zinner extrusion die,.thecrossfsectional area of .the

inner extrusion diebeingsmaller thanthe crosssectional Aarea Vof the.annular extrusion die, Ythe pipe of .thermoplastic material .coming into,con-

tact with the,continuouscoreofexplosive chargel and'exertingaslightpressure ,on itbyeffectfof a traction exerted on said .pipewhenhot.

Y.@References :on fo'llowing page) References Cited in the file of thispatent Number UNITED STATES PATENTS Name Date 5 Mignon Feb. 14, 1882Hamon Nov. 20, 1883 Webb Jan. 14, 1908 Sutton July 26, 1921 Bond Apr.18, 1933 lo Short Mar. 18, 1941 Wiley et al. Aug. 4, 1942 Caldwell Nov.28, 1944 Number Number Name Date Imber Aug. 14, 1945 Johnson Oct. 1,1946 Slaughter Nov. 2, 1948 Selvidge Feb. 21, 1950 Prendergast Mar. 28,1950 FOREIGN PATENTS Country Date Great Britain Aug. 7, 1928 GreatBritain July 1, 1949 France Mar. 6, 1944

